Add tests to ensure that we documented all signals

src/tests/doc/test_signals.py

@@ -0,0 +1,32 @@
+import glob
+import importlib
+import os
+from contextlib import suppress
+
+import pytest
+from django.conf import settings
+from django.dispatch import Signal
+
+from pretix.base.signals import DeprecatedSignal
+
+here = os.path.dirname(__file__)
+doc_dir = os.path.join(here, "../../../doc")
+
+plugin_docs = ""
+for f in glob.glob(os.path.join(doc_dir, "development/api/*.rst")):
+    with open(f, "r") as doc_file:
+        plugin_docs += doc_file.read()
+
+
+@pytest.mark.parametrize("app", settings.CORE_MODULES)
+def test_documentation_includes_signals(app):
+    with suppress(ImportError):
+        module = importlib.import_module(app + ".signals")
+        missing = []
+        for key in dir(module):
+            attrib = getattr(module, key)
+            if isinstance(attrib, Signal) and not isinstance(attrib, DeprecatedSignal):
+                if key not in plugin_docs:
+                    missing.append(key)
+
+        assert not missing, "The following signals are undocumented: %r" % missing